The use of metallic foils, such as aluminum foil,
packaging material requires that coatings and/or inks be applied to the surface of the foil, either to protect the foil or to provide a decorative surface.
Traditionally, clear coatings and inks for such purposes have been organic solvent-based. With increased environmental concerns, there is a need to replace these organic solvent-based inks and coatings with water-based materials.
While water-based inks and coatings for metallic foils are available, they are not without problems. Such materials require higher drying temperatures and/or increased drying times than the more traditional organic solvent-based materials. If sufficient drying of the known water-based inks and coatings does not occur, unacceptably objectional ammonia residue odor remains. This has proved to be an especially difficult problem for older coating and printing lines, which were not designed for the temperatures and drying times required by such water-based inks and coatings.
Another problem with water-based inks and coatings for metallic foils is their relatively low water resistance when dried. Since foil packaging materials must be compatible with food products, the low water resistance of known water-based inks and coatings makes them unacceptable for such purposes.
In U.S. Pat. No. 4,783,497, the disclosure of which is incorporated herein by reference, water-based polyester coating compositions containing an alkylated amino resin are described. These compositions do provide good adhesion, flexibility, water resistance and low odor. A problem with these compositions, however, is the relatively high temperatures of from about 250.degree. to about 300.degree. F. required to cure the compositions to water resistance.
It is thus a primary objective of the present invention to provide a water-based ink or coating composition which has the required adhesion, flexibility, water resistance and low odor to be an acceptable material for coating onto metallic foils and which can be cured to water resistance at substantially lower temperatures than other coating compositions having these properties.